1. Field of the Invention
The general field of the invention relates to a unique electromagnetic antenna which can be used for radiating and non-radiating electromagnetic devices. Embodiments of the invention relate generally to antenna structures and, more particularly, to antenna structure having a radiating element structured on LCD, and to antenna having an array of such radiating elements.
2. Related Arts
Various antennas are known in the art for receiving and transmitting electro-magnetic radiation. Physically, an antenna consists of a radiating element made of conductors that generate radiating electromagnetic field in response to an applied electric and the associated magnetic field. The process is bi-directional, i.e., when placed in an electromagnetic field, the field will induce an alternating magnetic fields in the antenna and electric field would be generated between the antenna's terminals. The feed or transmission lines or network, conveys the signal between the antenna and the tranceiver. The feed network may be different type of transmission lines, bends, power splitters, filters and may also include antenna coupling networks and/or waveguides. An antenna array refers to two or more antennas coupled to a common source or load so as to produce a directional radiation pattern. The spatial relationship between individual antennas contributes to the directivity of the antenna. An antenna array in general is basically applying the sampling theorm in a spatial world, thus any aperture antenna such as horn antennas, reflectors or any other shape of open aperture, can be designed to produce similar radiation petterns and gain, using an array which consists of a certain type of element, which is a basic antenna element, and arranged in a grid, rectangular or other with predifined spacing between the elements.
While the antenna disclosed herein is generic and may be applicable to a multitude of applications, one particular application that can immensely benefit from the subject antenna is the reception of satellite television (Direct Broadcast Satellite, or “DBS”), both in a stationary and mobile setting. Fixed DBS, reception is accomplished with a directional antenna aimed at a geostationary satellite. In mobile DBS, the antenna is situated on a moving vehicle (earth bound, marine, or airborne). In such a situation, as the vehicle moves, the antenna needs to be continuously aimed at the satellite. Various mechanisms are used to cause the antenna to track the satellite during motion, such as a motorized mechanism and/or use of phase-shift antenna arrays. Further general information about mobile DBS can be found in, e.g., U.S. Pat. No. 6,529,706, which is incorporated herein by reference.
One known two-dimensional beam steering antenna uses a phased array design, in which each element of the array has a phase shifter and amplifier connected thereto. A typical array design for planar arrays uses either micro-strip technology or slotted waveguide technology (see, e.g., U.S. Pat. No. 5,579,019). With micro-strip technology, antenna efficiency greatly diminishes as the size of the antenna increases. With slotted waveguide technology, the systems incorporate complex components and bends, and very narrow slots, the dimensions and geometry of all of which have to be tightly controlled during the manufacturing process. The phase shifters and amplifiers are used to provide two-dimensional, hemispherical coverage. However, phase shifters are costly and, particularly if the phased array incorporates many elements, the overall antenna cost can be quite high. Also, phase shifters require separate, complex control circuitry, which translates into unreasonable cost and system complexity.
A technology similar to DBS, called GBS (Global Broadcast Service) uses commercial-off-the-shelf technologies to provide wideband data and real-time video via satellite to a diverse user community associated with the US Government. The GBS system developed by the Space Technology Branch of Communication-Electronics Command's Space and Terrestrial Communications Directorate uses a slotted waveguide antenna with a mechanized tracking system. While that antenna is said to have a low profile—extending to a height of “only” 14 inches without the radome (radar dome)—its size may be acceptable for military applications, but not acceptable for consumer applications, e.g., for private automobiles. For consumer applications the antenna should be of such a low profile as not to degrade the aesthetic appearance of the vehicle and not to significantly increase its drag coefficient.
Current mobile systems are expensive and complex. In practical consumer products, size and cost are major factors, and providing a substantial reduction of size and cost is difficult. In addition to the cost, the phase shifters of known systems inherently add loss to the respective systems (e.g., 3 dB losses or more), thus requiring a substantial increase in antenna size in order to compensate for the loss. In a particular case, such as a DBS antenna system, the size might reach 4 feet by 4 feet, which is impractical for consumer applications.
As can be understood from the above discussion, in order to develop a mobile DBS or GBS system for consumers, at least the following issues must be addressed: increased efficiency of signal collection, reduction in size, and reduction in price. Current antenna systems are relatively too large for commercial use, have problems with collection efficiency, and are priced in the thousands, or even tens of thousands of dollars, thereby being way beyond the reach of the average consumer. In general, the efficiency discussed herein refers to the antenna's efficiency of collecting the radio-frequency signal the antenna receives into an electrical signal. This issue is generic to any antenna system, and the solutions provided herein address this issue for any antenna system used for any application, whether stationary or mobile.
There are several types of microstrip antennas (also known as a printed antennas) the most common of which is the microstrip patch antenna or patch antenna. A patch antenna is a narrowband, wide-beam antenna fabricated by etching the antenna element pattern in metal trace bonded to an insulating substrate. Some patch antennas eschew a substrate and suspend a metal patch in air above a ground plane using dielectric spacers; the resulting structure is less robust but provides better bandwidth. Because such antennas have a very low profile, are mechanically rugged and can be conformable, they are often mounted on the exterior of aircraft and spacecraft, or are incorporated into mobile radio communications devices.
An advantage inherent to patch antennas is the ability to have polarization diversity. Patch antennas can easily be designed to have Vertical, Horizontal, Right Hand Circular (RHCP) or Left Hand Circular (LHCP) Polarizations, using multiple feed points, or a single feedpoint with asymmetric patch structures. This unique property allows patch antennas to be used in many areas types of communications links that may have varied requirements.
FIG. 1 illustrates an example of a microstrip antenna of the prior art. As shown in FIG. 1, four conductive patches 105-120 are provided over dielectric 130. A base “common” ground conductor is provied below the dielectric 130, but is not shown in FIG. 1. Conductive lines 105′-120′ provide electrical connection to main line 140, which is connected to a central feed line 145.
A liquid crystal display (commonly abbreviated LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. Each pixel of an LCD consists of a layer of perpendicular molecules aligned between two transparent electrodes, and two polarizing filters, the axes of polarity of which are perpendicular to each other. With no liquid crystal between the polarizing filters, light passing through one filter would be blocked by the electrodes. The surfaces of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using a cloth (the direction of the liquid crystal alignment is defined by the direction of rubbing).
Before applying an electric field, the orientation of the liquid crystal molecules is determined by the alignment at the surfaces. In a twisted nematic device (the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular, and so the molecules arrange themselves in a helical structure, or twist. Because the liquid crystal material is birefringent, light passing through one polarizing filter is rotated by the liquid crystal helix as it passes through the liquid crystal layer, allowing it to pass through the second polarized filter. Half of the light is absorbed by the first polarizing filter, but otherwise the entire assembly is transparent.
When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field, distorting the helical structure (this is resisted by elastic forces since the molecules are constrained at the surfaces). This reduces the rotation of the polarization of the incident light, and the device appears gray. If the applied voltage is large enough, the liquid crystal molecules are completely untwisted and the polarization of the incident light is not rotated at all as it passes through the liquid crystal layer. This light will then be polarized perpendicular to the second filter, and thus be completely blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts, correspondingly illuminating the pixel.
FIG. 2 illustrates a cross-section of an LCD of the prior art. As shown in FIG. 2, the LCD 200 comprises a back panel 205 which may be glass, a front panel 210 which is also generally made of glass, a liquide crystal 215 positioned between the two panels, a back electrode 220, which may be indium/titanium/oxide (ITO), aluminum, etc, and front electrodes 225, which are coupled to potential 230 and are generally made of ITO. The potential 230 may be applied individually to each electrode 225. As potential is applied to an electrode 225, the liquide crystal below it changes its orientation and, thereby changes the local dielectric constant between the powered electrode and the section of the rear electrode corresponding to the area of the front electrode.